We want 3 Tbsp vinegar, then 1/2 cup total more liquid. It could be all wine, but since I rarely have wine in the house, I use a combination of brandy and water.
Grind dry ingredients in large mortor and pestle
Crush garlic to a paste in the dry ingredient powder.
Add wet ingredients in a reaction free container, and refrigerate for at least 24 hours. Mustard is quite bitter until the vinegar has done it's work.
I think this would be excellent with some horseradish, but I have not tried that yet. I'd get fresh horshradish root, and grind it into a paste along with the garlic.